The blacktip reef shark, an example of aspecies that has been affected by humans.Image: Macquarie University

A study by researchers from the University of California - Santa Barbara (UCSB) and Macquarie University into the human impacts on the health and well being of marine ecosystems has recently been published in the journal American Naturalist.

The study reports that when hunted by large predators, such as sharks and snapper, small fish hide and move around less. When predator numbers are seriously reduced, their prey move greater distances, take more risks, and change feeding behaviours. These behavioural responses in prey species also drive significant changes in the balance of ecosystems.

The study looked at coral reefs of the central Pacific Ocean's northern Line Islands, a small equatorial archipelago thousands of miles from the nearest landmass. Predators had been heavily fished near some islands and virtually never fished near others.

Lead author on the research, Dr Elizabeth Madin, said they were able to see first-hand how fishing had decimated populations of sharks and other predators.

"By removing predators and changing the grazing behaviour of small fish, there were dramatic changes in the seaweed patterns on coral reefs, giving the reefs a new look," Dr Madin said.

"Seaweed is important because lush areas of seaweed inhibit the settling and growth of coral - the critically important engineers of the reef. By changing where seaweed grows, fishing may be limiting where coral can grow."

Previously with UCSB's Department of Ecology, Evolution & Marine Biology, Dr Madin was based at Macquarie University when parts of the research were undertaken. She is now a US National Science Foundation International Postdoctoral Fellow with the UTS Faculty of Science.

Her co-authors on the paper include the UCSB's Professor Robert Warner and Professor Steven Gaines, and Macquarie University's Dr Joshua Madin.